Update Dockerfile

Dockerfile

@@ -7,8 +7,9 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 COPY . .
 
+# Set default port, override with environment variable if needed
 ENV PORT=8501
 
-EXPOSE $PORT
+EXPOSE 8501
 
-CMD ["streamlit", "run", "app.py", "--server.port", "$PORT"]
+CMD streamlit run app.py --server.port ${PORT}